This invention relates to machines and sub-assemblies thereof for manufacturing hollow articles from thermoplastic materials by blow molding.
Blow molding is a fabrication method for hollow thermoplastic shapes.
Two general classes of plastic products are made in this mannerxe2x80x94packaging products and technical parts. Packaging products include such items as bottles, jars, jugs, cans, and the like. Technical parts include automotive components such as bumpers, fuel tanks, functional fluid containers, ducting, and the like.
The blow molding process can be of two general types: extrusion blow molding and injection blow molding. In extrusion blow molding, a parison is lowered between mold halves from an extruder. The mold halves then close around the parison, and the mold is transferred to a blowing station where the parison is then expanded against a mold cavity by introduction of a blowing gas, usually air. In injection molding, a thermoplastic material is first injection molded into a preform parison which is then transferred to a blow mold and expanded in the same manner as in an extrusion blow molding process. In both cases, however, the parison is transported from a parison receiving station to a blow molding station to complete the fabrication of a hollow plastic article.
In continuous extrusion, a molten parison is produced from an extruder die without interruption, and a segment thereof is severed and positioned into a mold. In many blow molding machines, the molds are moved from station to station on rotating vertical wheels, on a rotating horizontal table, or with a reciprocating action of a shuttle mechanism.
Most of the current blow molding machines utilize the reciprocating mold concept according to which the molds are shuttled back and forth from the parison receiving station to the blow molding station. A major drawback of the reciprocating mold concept, however, is a limitation on production rate because of the multiple stations in the process, namely the parison insertion station, the blow molding station, and the cooling station. Another drawback of the reciprocating mold concept is that many heavy parts must be moved during the blow molding process. For example, an entire shuttle mechanism with multiple blow molding stations and parison receiving stations may need to be moved during the process. Another concern present in many existing blow molding machines is the number of moving parts in the machines.
A further problem with most blow molding concepts is that after the parison is positioned in a mold, the mold is then taken to a separate blowing station where the air or other fluid is injected into the parison to form the hollow article. The time required to move the mold from the station where the parison is positioned to the blow molding station creates stress on the parison before inflation because of cooling that occurs with the parison, which makes the inflation process more difficult.
In view of the relatively large commercial demand for various types of plastic articles, it would be desirable to have a blow molding machine of relatively high capacity that can produce high quality articles at a relatively low cost, and which avoid the problems discussed. The present invention satisfies this desire by reducing the amount of tooling, reducing the mass of moving parts, reducing the traveling distance of moving parts, reducing the stress on the parison before inflation, minimizing in-mold time for the hollow article to improve cavity utilization, and maximizing cooling effectiveness.
The present invention provides a blow molding machine capable of relatively high production rates at relatively low cost, which requires fewer moving parts and reduces stress on the parison.
The foregoing advantages are achieved by a blow molding machine having a single blow molding station that also is adapted to receive a parison. In particular, the blow molding machine comprises a base, a reciprocating shuttle mechanism supported by the base, a single blow molding station supported by the base, which is adapted to receive a parison for forming the hollow article at the blow molding station, a pair of cooling stations supported by the base on flanking sides of the blow molding station, a pair of reciprocating blow pin carriages spaced from one another, each of which is connected to the shuttle mechanism and is indexable between the blow molding station and one of the cooling stations. Each blow pin carriage comprises one or more blow pin assemblies whose vertical positions relative to the shuttle mechanism are independently adjustable between a rest position and a blow position. The blow molding station is fixed relative to the base, and the blow pin carriages are indexed to the blow molding station alternatively. The shuttle mechanism, which moves in a substantially horizontal plane relative to the base, may be driven and controlled in any convenient manner, e.g., by a hydraulic driving mechanism, a mechanical driving device, or any other driving device as is known in the art, such as a pneumatic cylinder, a solenoid device, or the like.
The present invention may be adapted to mold a single hollow article or multiple hollow articles at a time. For example, if a single hollow article is to be formed, a single parison is received by a mold configured with a single cavity to form a single hollow article, such as a bottle. If multiple articles are to be formed, a single parison combined with a multiple cavity mold, or multiple parisons with a multiple cavity mold may be used.
As discussed above, parison used in blow molding can either be extruded, or preformed. The present blow molding machine may be arranged to accept either extruded parison or preforms into the blow molding station.
Once the parison is received at the blow molding station, the mold, which typically comprises two complementary mold halves, is closed around the parison, and in the case of an extruded parison, pinches shut one end of the parison. A blow pin carriage that comprises at least one blow pin assembly is juxtaposed relative to the mold, and the blow pin is moved to a blow position and is engaged with the mold. When the blow pin carriage is juxtaposed relative to the mold, the blow pin assembly can be engaged with the open end of the parison. Air or some other gaseous fluid is injected into parison, which causes the parison to be inflated inside the mold so as to form the molded article. The mold is then opened, and the molded hollow article is carried by the blow pin carriage to one of a pair of cooling stations that flank the molding station.
The present invention, when adapted to receive extruded parison, also preferably includes a top plate that is supported by the shuttle mechanism and is adapted to move in a substantially horizontal plane relative to the base. This top plate defines one or more apertures through which the parison may be received to be formed into a hollow article. As the formed hollow article is carried from the blow molding station to the cooling station, flash produced during the molding operation is supported by the top plate, and particularly by an edge of one of the apertures in the top plate.
The cooling station is comprised of a holding mechanism, which may be any device or arrangement that can be used to receive and grasp a molded hollow article as is known in the art. Preferably, this holding mechanism includes one or more pairs of gripping rails juxtaposed relative to one another and spaced to receive and grasp a molded hollow article in between the gripping rails. After the molded hollow article is received and grasped by the holding mechanism, such as the gripping rails, the blow pin assembly is retracted downwardly from the blow position to a rest position such that the blow pin assembly is sufficiently lowered out of the hollow article so that it may be moved in a substantially horizontal plane back to the, blow molding station, and away from the cooling station for the next operating cycle. Alternatively, if the molded hollow article is sufficiently cooled during its transport from the blow molding station to the cooling station, the hollow article may be ejected upon reaching the cooling station.
After a hollow article is molded, and as it is being carried to one of the cooling stations by a first of the blow pin carriages, the second blow pin carriage is indexed with the blow molding station, is raised to a blow position, and engaged with the mold. A parison is then inflated and molded in the same manner as previously discussed. Once this second hollow article is molded, and the mold is opened, the molded hollow article is carried by the blow pin carriage to the cooling station on the opposite flank from the previous cooling station. The first blow pin carriage is shuttled back to the blow molding station as the second hollow article is transported to the opposite cooling station. This alternating process cycle is continued as long as desired.
In one embodiment of the present invention, a formed hollow article is held at the cooling station until the next formed hollow article is carried by the blow pin carriage to the cooling station and knocks the first hollow article out of the cooling station holding mechanism. For example, where the holding mechanism is the pair of gripping rails juxtaposed relative to one another and spaced to receive and grasp a molded hollow article in between the rails, the next formed hollow article is carried to and in between the rails. As the second molded hollow article is carried between the two rails, it pushes the previous hollow article out of the cooling station into a bin or the like.